440 SCIENCE PROGRESS 



and Cundall's result that ozone is as rapidly formed from oxygen 

 dried with phosphoric oxide as from the gas which had been 

 desiccated with sulphuric acid only. Baker's observations on 

 the action of dried ozone on mercury do not, however, harmonise 

 with Shenstone's statement. In view of the fact that purified, 

 dried chlorine does not appear to differ from the moist gas in its 

 behaviour towards the metal mercury, it is, in the opinion of 

 the writer, highly desirable that further experiments should be 

 made on the action on mercury of ozone dried to different extents. 

 Shenstone was not satisfied with his earlier results ; accord- 

 ingly, in 1897, he returned to the examination of the main problem 

 of his former research. In preparing the oxygen and in 

 desiccating it he took the most minute precautions. The care 

 taken to eliminate every conceivable source of error made it 

 necessary to use a very complex and fragile apparatus, which 

 unfortunately broke after three experiments had been performed. 

 These experiments were considered sufficient, in view of the 

 care that had been taken in carrying them out, to justify 

 the conclusion that all previous statements on the subject of the 

 research were wrong. The result he obtained was that the 

 stability of ozone prepared from oxygen thoroughly dried by 

 exposure to phosphoric oxide is so small that only o'2 per cent, 

 of the oxygen can be changed into ozone by the silent discharge. 

 On the other hand, ozone prepared from moist oxygen he found 

 to be extremely stable at the ordinary temperature. Shenstone 

 concluded that water vapour prevents the reversion of ozone 

 into oxygen — that water, in fact, is in this case a negative 

 catalyst. Armstrong refused to accept Shenstone's conclusion, 

 his contention being that oxides of nitrogen had been formed by 

 the action of the silent discharge on the oxygen and a small 

 quantity of adventitious nitrogen contained in it and that the 

 oxides of nitrogen, being powerful catalytic agents, rendered the 

 ozone unstable. There can be no doubt that Armstrong's 

 explanation is right and in the opinion of the writer Shenstone 

 would have come to precisely the same conclusion if, instead of 

 being satisfied with three experiments, he had investigated the 

 effect of varying all the conditions of the experiment ; he would 

 then have discovered that the stability of the ozone was not only 

 dependent on the amount of water vapour it contained but also 

 on the length of time during which the oxygen had been sub- 

 mitted to the action of the discharge. It is not at first sight clear 



